This invention relates to a device for measuring the output power of an edge coupled unstable resonator and, more particularly, the invention is concerned with providing a calorimeter which includes a flat absorbing metal plate positioned perpendicular to the optical axis of the resonator and includes a variable aperture thereby permitting the collection of information as to the lasing intensity distribution as a function of the mode geometry.
The conventional method for extracting laser power from an unstable resonator is by diffraction past the boundaries of the smallest cavity mirror. This so-called "edge coupling" technique is generally accomplished in one of two ways, either a small "finite edge" coupling mirror is suspended in the optical axis or a 45.degree. mirror with a hole parallel to the optical axis is positioned in the optical axis. An optical window is required when the laser cavity region is below atmospheric pressure.
The mode geometry of an edge coupled unstable resonator is determined by the magnification of the mirrors and the cross sectional shape of the coupling mirror. There will be an optimum mode geometry for extracting maximum power from a specified gain region. The gain distribution in an arc driven continuous wave (CW) HF laser, for instance, cannot currently be modeled theoretically in terms of the various experimental parameters such as gas flow rates, plenum pressure, arc current and voltage etc. The measurement of the output power for different mode geometries presently requires several expensive mirrors and, typically, a vacuum output window of good optical quality. Thus, it would be most desirable and beneficial to be able to determine the optimum mode geometry for an unstable resonator by measuring experimentally the variation of output power for different mode geometries without the use of a coupling mirror or optical output window.